Lessons on Alloys, Amalgams, and Pleonasms (2)

Keith P. Walsh is spreading drivel again (August 25, 2007). As usual
he is confused, and he may be confusing readers of both the

sci.med.dentistry and sci.materials newsgroups. He needs to take some
lessons rather than try to give them.
Point 2: The technical definition for an amalgam (a noun describing a
material)
The Metals Handbook, Desk Edition (2nd, 1998) defines an amalgam as:
"a dental alloy produced by combining mercury with alloy particles of
silver, tin, copper, and sometimes zinc".
The single volume, 1948 edition of the Metals Handbook, defines an
amalgam more simply just as: "a mercury-base alloy".
I believe that the time-tested (almost sixty year old) Metals Handbook
definition is a sensible description for what an amalgam is.
Based on the above definitions:
Point 3: An amalgam is an alloy, and an amalgam implies the presence
of mercury.
The Metals Handbook started out as a single volume. It grew over ten
editions into a rather authoritative collection of about two dozen
thick reference books that take up an entire shelf. You can typically
find it in a university library or a large public library.
More recently the Metals Handbook was renamed simply as the ASM
Handbook, since its coverage is being broadened to include other
materials that formerly were covered in another series called the
Engineered Materials Handbook. These handbooks are the consensus
result of a large collective enterprise involving many committees and
the volunteer efforts of hundreds of members.
The Desk Editions are affordable versions condensed down to single
volume. I cited it because I have it on my bookshelf.
Pittsburgh Pete
DISCLAIMER
We do not believe what we write, and neither should you. Information
furnished to you is for topical (external) use only. This information
may not be worth any more than either a groundhog turd, or what you
paid for it (nothing). The author may not even have been either sane
or sober when he wrote it down. Do not worry, be happy.

Keith is a wonder, of sorts, isn't he.
There are some people in life that are best avoided, and Keith P. Walsh
is one of them.
Good luck, Pete.
Good to see you still posting, and doing your best to mitigate the
misinformation and distortion.
Jim
snipped-for-privacy@hotmail.com wrote:

That may be because I have a habit of embarrassing people by exposing
their ignorances.
I'll try an example.
Pittsburgh Pete says, "An amalgam is an alloy, and an amalgam implies
the presence of mercury."
That "an amalgam" has come to imply mercury (note that even Pete only
says "implies" and not "requires"), especially in the dental
profession, is because mercury amalgams are the most common.
But mercury amalgams are NOT the only type of amalgam, as you can see
by extracts from the book, "Principles of Soldering", by Giles
Humpston and David M Jacobson, published by ASM International (April
2004) and endorsed by The Materials Information Society.
The parts which are of interest to us are:
Page 115 - Section 5.4.1 - Amalgams Based on Mercury
Page 116 - Section 5.4.2 - Amalgams Based on Gallium
"Gallium melts at 29 deg C and is therefore a potential base for
formulating very low-process-temperature amalgams without the toxic
hazard associated with mercury"
(Note, there's no mercury in these amalgams.)
Page 117 - Section 5.4.3 - Amalgams Based on Indium
"Indium is another liquid metal that can be considered as a base for
amalgam systems. "
(There's no mercury in these amalgams either.)
You can read all this at:
http://books.google.com/books?id=cQ6khQScBF4C&pg=PA103&dq=%22gallium+amalgam%22&sig=Um_AAj4cKineMZPCpE4sXOWq3Uw#PPP1,M1
So Jim, it is clear from the above that the term "mercury amalgam" is
NOT a pleonasm, because on its own the word "amalgam" is not
sufficient to distinguish between "mercury amalgams" in which the
liquid metal amalgamating agent is mercury, "gallium amalgams" in
which the liquid metal amalgamating agent is gallium, and "indium
amalgams" in which the liquid metal amalgamating agent is indium.
Now, do you agree with this?
Go on, answer that one simple question.
Do you agree that the term "mercury amalgam" is NOT a pleonasm?
How about you Pittsburgh Pete?
(Or even you Steven Bornfield?)
Keith P Walsh

I see you are still the same fellow, boring in with the same standard
challenging responses.
You are truly one of the people in life best avoided.
PLONK !
I've created a special kill filter just for you.
Jim
Keith P Walsh wrote:

Read and learn Jimbo. Read and learn.
If you mix together different metals at a temperature which is above
the melting point of only one of the metals in the mix, and you allow
the mixture to harden, then what you end up with is an inhomogeneous
mixture of dissimilar metals, an example of which is shown at:
http://book.boot.users.btopenworld.com/setting.htm
If you want to create such a material working at room temperature then
you have to use mercury as the molten (liquid) metal component in the
mix, because mercury is the only metal that is in the liquid state at
room temperature.
However, if you work at a little over 30 degrees celsius then it is
possible to use liquid gallium to mix with solid pieces of other
metals and create a mixture of metals which, because of the way in
which it has been formed, will have a similarly inhomogeneous
microstructure to that described above.
And of course if you can work at a temperature around 160 degrees
celsius (not much use for patients in dental surgeries) then you can
produce other solid metal mixtures, again with similarly inhomogeneous
microstructures to those described above, by using liquid indium to
"amalgamate" solid bits of other metals.
If on the other hand you mix together different metals at a
temperature which is well above the melting points of ALL of the
metals in the mix, and you mix them thoroughly before allowing the
mixture to solidify by cooling at a controlled rate, then what you get
is a solid mixture of metals which does not have the same degree of
material inhomogeneity as the materials desgribed above. What you get
is a different type of mixture of metals which has a much more
homogeneous microstructure whereby it would not be possible to show
the relative positions of the atoms of the different metals at the
scale of the diagram indicated above.
Now, one important point to note is that it doesn't really make any
difference what we call these materials, because of their different
physical structures the two different types of material will
distinguish themselves naturally by differences in their physical
behavior. And these differences are determined by Nature, not by the
names which anyone might prefer to give them.
For example, you would expect the thermoelectric behavior of these two
types of material to be different as a consequence of the differences
in their internal sctructure.
However, at this point it would be convenient to be able to identify
the two different types by giving them different labels, or "names".
I think it makes sense to call the first ype of material, (where bits
of solid metal are "amalgamated" by mixing them with a liquid metal
"amalgamating agent" - which might be mercury, gallium or indium) an
"amalgam". And in fact I do rather suspect that this usage may
actually be the true origin of the word amalgam - even if it did arise
through the discovery and use of mainly "mercury amalgams".
And I think it also makes sense to call the other type of material,
where all of the metals are mixed in their liquid states, true alloys
- or simply "alloys".
Remember that it doesn't make any difference if Pittsburgh Pete wants
the "amalgams" to be called "alloys" as well ( - at least he appears
to have given up on the idea that an amalgam must have mercury), the
amalgams will distinguish themselves naturally from the true alloys by
the differences in their physical behaviors.
And you can see that this must be true by considering the
thermoelectric properties of the materials.
A quick reminder of the thermoelectric effect can be seen at:
http://book.boot.users.btopenworld.com/thermo2.htm
The relevant point to understand here is that if you put dissimilar
metals in contact with each other and maintain the contact points at
different temperatures then an electrical current will flow, and the
current will continue to flow for as long as the temperature
difference is maintained. This phenomenon of course runs contrary to
the popular myth that in order for dissimilar metals in contact with
each other to produce an electrical current they must become involved
in an electrolytic reaction. (A myth which seemed particularly
prevalent amongst members of the dental profession by the way - at
least before I came along and started pointing out that it isn't
true.)
This thermoelectric effect is also the explanation for what happens
when bits of one metal are encased within another metal and subjected
to a temperature gradient. You can see a graphical representation of
this effect at:
http://www.elektrotechnik.hs-magdeburg.de/Mitarbeiter/hinken/news/N6.htm
(figure d is particularly instructive)
The temperature gradient shown induces a thermoelectric eddy current
around the inclusion, and this produces an electromagnetic field which
extends outside the surfaces of the surrounding material and can be
detected using sensitive instruments.
The presence of this phenomenon in Nature is used to detect inclusions
of metals inside other metals.
It works if the inclusion and the surrounding material are both pure
(but dissimilar) elemental metals.
And it also works if the inclusion and the surrounding material are
dissimilar alloys.
But it doesn't work for a single true alloy if there is no inclusion
of a dissimilar metallic composition inside it. This is because the
component metals in a true alloy are too homogeneously mixed for the
effect being detected to arise.
Now, because of their inhomogeneous internal structures you would
expect this effect to arise in amalgams (including dental amalgams
made with mercury). But, as I have already said, you would not expect
it to arise in a true alloy.
Get the message?
At this point I should ask if you know whether or not experimental
investigations have ever been carried out in order to measure the
thermoelectric behavior of a typical dental amalgam, and to compare it
with the thermoelectric behavior of a true alloy.
But I already know that you don't, so I shall just point out to you
that therein lies your ignorance.
Keith P Walsh

Keith:
Your combination of ignorance and arrogance is truly appalling. The
phrase you can't find to describe a "mixture of metals which has a
much more homogeneous microstructure whereby it would not be possible
to show the relative positions of the atoms of the different metals"
is simply called a phase. A particular alloy that starts out from a
homogeneous liquid may not be a single phase once it solidifies.
Why don't you just step away from the keyboard, go down to the
library, and learn something about materials before you go
pontificating to the world? Michael F. Ashby and D.R. H. Jones have
written two good books on Engineering Materials. Engineering Materials
2 (An introduction to microstructures, processing, and design) is
worth reading, if you want to actually learn about how nature works.
Pittsburgh Pete
DISCLAIMER
We do not believe what we write, and neither should you. Information
furnished to you is for topical (external) use only. This information
may not be worth any more than either a groundhog turd, or what you
paid for it (nothing). The author may not even have been either sane
or sober when he wrote it down. Do not worry, be happy.

Pete,
Experience has led me to believe that there isn't any book in any
library anywhere in the world which contains any scientific
information at all concerning the thermoelectric properties of the
inhomogeneous mixtures of dissimilar metals commonly used in
restorative dentistry.
I would be delighted if you could prove me wrong.
Keith P Walsh
PS, can I take it we are now agreed that the term "mercury amalgam" is
NOT a pleonasm?

Log in

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.